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Tuesday, June 6, 2023

Psoas Major Provides Stability and Mobility to the Hip Joint

Brent Brookbush

Brent Brookbush


Research Review: Psoas major provides stability and mobility of the hip joint

By Stefanie DiCarrado DPT, PT, NASM CPT, CES, & PES

Edited by Brent Brookbush DPT, PT, COMT, MS, PES, CES, CSCS, ACSM H/FS

Original Citation: Yoshio, M., Murakami, G., Sato, T., Sato, S., Noriyasu, S. (2002). The function of the psoas major muscle: Passive kinetics and morphological studies using donated cadavers. Journal of Orthopaedic Science 7:199-207 - ABSTRACT

Why is this relevant?: The psoas major (PM) is often linked to low back and hip pain, and has been commonly labeled a "problem" muscle by practitioners. Some practitioners have gone as far as labeling injury to this muscle (with accompanying low back and hip symptoms) as a syndrome: Psoas Syndrome . The PM can flex and externally rotate the hip, and perform contralateral rotation, ipsilateral flexion, extend the spine in conjunction with an anterior pelvic til, or flex the spine on a fixed pelvis. Less is known about its ability to stabilize the lumbar spine, sacrum and hip. Kimura et al (1991), as cited in this study, found an abundance of Type I (fatigue resistant) muscle fibers within PM, indicating a possible role stability over force production. The assertion of the PM as a stabilizer supports findings by Stewart McGill, who has written about the different functions of deep versus more superficial motor units of the PM (1, 2).

The Psoas Major as it courses from its origin to insertion

Study Summary

Study DesignPassive Kinetic Descriptive Experimental
Level of EvidenceLevel VI: Evidence from a single descriptive or qualitative study
Subject Demographics
  • Age: 70+ y.o at time of death
  • Gender:
    • Force & Pressure Group: 3 females, 7 males
    • Tendon Changes Group: 8 females, 17 males

  • Characteristics: 35 cadavers with identifiable psoas major muscles (PM); no significant osteoarthritis on any specimen
  • Inclusion Criteria: NA
  • Exclusion Criteria: NA
Outcome Measures
  • Degree of hip flexion where PM tendon no longer contacts the femoral head and pelvic surface
  • Degree of hip flexion where the femoral head is hidden by pelvic acetabulum
  • Tensile force and pressure on PM or tendon with a pull toward muscle origin (supine)
    • Measured at 7 different degrees of hip flexion
      • 0º, 15º, 30º, 45º, 60º, 75º, 90º degrees

    • Pressure only measured at 8 different sites along length of the PM tendon
      • 2cm (s2) and 1cm (s1) superior of the iliopectineal eminence (a point where the long axis and transverse line crossed - considered a "pulley" of the muscle tendon)
      • At the iliopectineal eminence (s0)
      • 1cm (i1), 2cm (i2), 3cm (i3), 4cm (i4), and 5cm (i5) inferior from the eminence level

  • PM tendon lost contact
    • With femoral head: 7º-19º (avg 14º) of hip flexion
    • With iliopectineal eminence: 42º-67º (avg 54º) of hip flexion

  • Femoral head hidden in acetabulum
    • 25º-53º (avg 39º) of hip flexion

  • Tensile force and pressure on bony surface during hip flexion
    • Force & pressure on femoral head and pelvis strong at 0-30º hip flexion, weak at 60º-75º
    • Max tension: 15º hip flexion (in 60% of measurement sites)
    • Pressure strongest at 0º; weak over 60º
    • Large force decrease from 30º-60º
    • Consistent decrease in force with increased hip flexion beyond 30º
    • Greater differences in pressure on the pelvis than on femur between individuals

ConclusionsThe PM provides a posteriosuperior stabilization force to the femoral head in positions with less than 15º hip flexion. Beyond 60º hip flexion, the PM contributes mostly to hip flexion and provides no stabilization of the femoral head
Conclusions of the ResearchersPM acts phasically to erect the lumbar vertebral column. At the hip, the PM offers greatest stabilization to the femoral head from 0-15º hip flexion. Beyond 15º hip flexion, the PM acts less as a stabilizer from 15-45º hip flexion and then more as a mobilizer contributing to hip flexion from 45-60º.

Psoas Major

Review & Commentary:

Cadaver studies can provide interesting data that EMG, or imaging cannot. This particular study investigated specific angles of hip flexion where the psoas major (PM ) tendon does or does not touch the femoral head (recall the insertion of the PM is the lesser trochanter of the femur) - the tendon touching the femoral head suggests there is an element of stabilization with possible posterior force exerted.

This study provides strong evidence to suggest the PM functions as a hip stabilizer via a posterior and superior directed force on the femoral head from 0-15º hip flexion, and is a strong mobilizer of the femur, contributing to hip flexion at angles greater than 60º. The strengths of this study include a moderate sample size, specificity of outcome measures, and a standardized approach. A total of 35 cadavers provided 35 isolated specimen for analysis. The researchers separated the pelvis into 2 halves, utilizing those specimens with an intact hip joint and femur only. Everything below the knee and above the 11th thoracic segment were removed. This ensured full preservation of PM muscle and tendon. Researchers removed all soft tissue except the PM , joint capsule, and ligaments of the hip joint. The joint capsule was resected for easy viewing of the femoral head's motion. A custom built hinged device attached to the pelvis and femur allowed for precise, controlled and measurable hip motion. The device allowed for replication of the typical 60º angle formed by a line through the anterior superior iliac spine and the pubic tubercle that occurs with a normal pelvic tilt in standing. The authors provided clear images, descriptions of set up and descriptions of equipment, enabling replication in future studies.

The researchers measured the tension required to lift the femur approximately 1 cm at various hip flexed positions. To do this, they attached a traction device to the PM origin, along with a load cell strain gauge inserted into the tendon itself. Tension measurements at various positions of hip flexion provide insight into the force needed to move the femur by the PM . Measurements of pressure, attained by sensors inserted between the PM tendon and the femur/pelvis at eight different sites along the length of the PM tendon, provided information pertaining to a posterior, compressive force exerted on the bony surface (femoral head or pelvic eminence) at various hip flexion positions.

There were a few anomalies in the data, but the authors did not believe this decreased statistical significance. Interestingly, two specimens actually demonstrated increased tension from 75º-90º of hip flexion which is contradicts the majority of the data attained. Another interesting finding was a direct relationship between femoral neck shaft angle and pressure:. The specimen with the smallest neck shaft angle showed no pressure at 60º and above; whereas, a specimen with the greatest neck shaft angle showed moderate pressure and tension after 60º. Authors noted a side slip of the tendon at 45º which may be due to missing fascia and other muscles, an unfortunate side effect of such specimen isolation.

As mentioned in the Brookbush Institute's Psoas article, research by Bogduk indicates a dual functionality of the psoas: posterior fibers originating on the costal surface of the transverse process contributing more so to stabilization of the spine (and hip) and anterior fibers contributing more to spinal (and/or hip) movement (3). It would have been interesting for this study to build upon that research by focusing on posterior and anterior fibers separately.

Why is this study important?

This study is important because it provides evidence regarding the various roles the PM plays, relative to hip flexion angle.

How does it affect practice?

Clinicians should be aware of the varied roles of the PM, to hypothesize its activity and contribution to dysfunction and appropriate interventions based on that hypothesis. The PM appears to apply a stabilizing (superior and posterior) force during near neutral angles of hip flexion (0-15°). As hip flexion increases, the role of the psoas becomes more movement oriented. Dysfunctional movement patterns during motions with minimal hip flexion may require activation of the psoas for stabilization, whereas dysfunctional movement patters during motions with considerable hip flexion may require inhibition of the PM . Further, tension is greatest on the PM in 0º of hip flexion. Anyone with suspected injury to the PM may wish to avoid hip flexion from a neutral position while in the supine when the leg produces considerable torgue force at the hip.

How does it relate to Brookbush Institute Content?

The function and common dysfunction of the PM presents a challenge to analysis, as it performs both stabilizing and mobilizing functions depending on hip flexion angle. Further, the PM may present as overactive or under-active due to influence from activity of receptors in investing tissues (anterior longitudinal ligament, arcuate ligament, diaphragm, etc.) and reflexive changes in tone and/or synergistic recruitment patterns. In the Brookbush Institute's predictive model of Lumbo Pelvic Hip Complex Dysfunction (LPHCD) the PM has a propensity toward over-activity and adaptive shortening (excessive lordosis/anterior pelvic tilt in the overhead squat assessment) In the Brookbush Institute's predictive model of Sacroiliac Joint Dysfunction (SIJD) , the psoas is found to be asymmetrical: short and overactive one one side while long and under-active on the side exhibiting SIJ stiffness (asymmetrical weight shift on the overhead squat assessment ). Further research is needed to clarify the function of the psoas, and common maladaptive changes noted in dysfunction of the hip and lumbar spine.

The videos below address assessment and treatment of an overactive and/or adaptively short hip flexor complex along with activation of the of the Intrinsic Stabilization Subsystem .

Modified Thomas Test:

Manual Hip Flexor Stretch (Thomas Test Position):

Static Hip Flexoor Stretch:

Active Hip Flexor Stretch:

Dynamic Hip Flexor Stretch (Upright Lunge Series):

Transverse Abdominis TVA Isolated Activation:

Quadruped and Glute Activation Progression:

Hardest Quadruped Progression Ever:

Quadruped Crawl:


  1. Kimura, T., Kouda, M., Ishida, M. et al (1991) Myofibrous organization in human psoas major muscle. Journal of the Showa Medical Association 51:509-513
  2. Stuart McGill, Low Back Disorders: Second Ediction © 2007 Stuart M. McGill
  3. Bogduk N., Pearcy M., Hadfield G. Anatomy and biomechanics of the psoas major. Clinical Biomechanics 7:109-119
  4. Andrew Vleeming, Vert Mooney, Rob Stoeckart. Movement, Stability & Lumbopelivic Pain: Integration of Research and Therapy (c) 2007, Elsevier Limited

© 2016 Brent Brookbush

Questions, comments, and criticisms are welcomed and encouraged -